1. Field of the Invention
The present invention relates to system and method for mobile communication, and more particularly, to a mobile communication system and a mobile communication method that avoid delay in data transmission between a mobile node and a communication terminal.
2. Description of the Background Art
A standard Internet Protocol (IP) currently utilized is called Internet Protocol version 4 (IPv4). A next generation protocol for replacement of IPv4, Internet Protocol version 6 (IPv6), has now been under examination and inspection.
The mobile communication in accordance with IPv4 and IPv6, or, so-called Mobile IP, is controlled in the following procedures.
FIGS. 13 and 14 show conventional procedures for establishing communication between a partner appliance and a mobile node under IPv4. In FIGS. 13 and 14, the communication procedures are shown as {circle around (1)}-{circle around (4)}. {circle around (1)}-{circle around (4)} in FIG. 13 correspond to {circle around (1)}-{circle around (4)} in FIG. 14.
FIG. 14 shows a system to which the Mobile IP corresponding to IPv4 is applied. The system in FIG. 14 includes: a communication network NE, such as the Internet, that is a main network to which the IP is applied; IP sub-networks 10 and 20, such as local area network, to which the IP is applied; and a home agent HA, a foreign agent FA and a partner appliance PA connected to one another through communication network NE; and a mobile node MN.
Partner appliance PA and mobile node MN each are mobile information equipment such as IP telephone, video telephone or the like. Herein, for simplification of explanation, partner appliance PA is assumed to be information equipment that does not move. Home agent HA and foreign agent FA each are equipment such as a gateway, which receives data via communication network NE, understands the intention according to the situations, and performs processing based on an autonomous determination. Home agent HA and foreign agent FA correspond to stations that relay the communication between mobile node MN and partner appliance PA. Communication network NE connects partner appliance PA, home agent HA and foreign agent FA to one another. IP sub-networks 10 and 20 connect home agent HA and mobile node MN, and foreign agent FA and mobile node MN, respectively. Home agent HA is used when mobile node MN is in an area communicable via IP sub-network 10; whereas foreign agent FA is used when mobile node MN has moved out of the area and is now in another area communicable with foreign agent FA via IP sub-network 20. From the standpoint of IP sub-network 10 corresponding to home agent HA, IP sub-network 20 corresponds to a foreign link, and therefore, it is also called xe2x80x9ca foreign linkxe2x80x9d. Herein, IP sub-networks 10 and 20 are assumed to be wireless communication networks.
Assume that mobile node MN that was being connected to IP sub-network 10 corresponding to home agent HA moves in a direction indicated by a dashed arrow AR and comes to be connected to IP sub-network 20 to which foreign agent FA belongs. Mobile node MN has a home address HAD when it is being connected via IP sub-network 10 to home agent HA. Home address HAD is a global address that is an IP address of mobile node MN when it is in the area communicable via IP sub-network 10. When mobile node MN moves outside the area and comes to be connected via IP sub-network 20 to foreign agent FA, then mobile node MN acquires a care of address CAAD being also a global address. It then notifies home agent HA of the care of address CAAD via foreign agent FA, and receives, from foreign agent FA, a current address in the area where mobile node MN has moved in (hereinafter, referred to as a xe2x80x9cmoved addressxe2x80x9d) MAD as its temporary IP address. Moved address MAD is an address for uniquely identifying a corresponding mobile node MN. Care of address CAAD is an IP address of foreign agent FA belonging to an area where mobile node MN has moved in, and indicates a current connect point for the relevant mobile node MN. Accordingly, a message for mobile node MN is transferred to care of address CADD by home agent HA, and foreign agent FA receives the message and sends it to the mobile node MN. The detailed communication at this time will be described with reference to FIG. 13.
The message for mobile node MN from partner appliance PA is sent as follows. Specifically, when home agent HA receives, from partner appliance PA, xe2x80x9ccall setup requestxe2x80x9d for a message in accordance with ITU-T Q.931, etc. (recommendation by International Telecommunication Union; hereinafter, simply referred to as Q.931, etc.) ({circle around (1)}), it sends the call setup request as capsulated data to foreign agent FA by tunneling ({circle around (2)}). Foreign agent FA performs decapsulation of the received call setup request, and sends the resultant to mobile node MN ({circle around (3)}). In response to receipt of the call setup request, mobile node MN sends xe2x80x9ccall acceptedxe2x80x9d, xe2x80x9ccallxe2x80x9d and xe2x80x9cresponsexe2x80x9d to partner appliance PA, not via home agent HA, but via foreign agent FA belonging to the area where the mobile node MN has moved in ({circle around (4)}). Hereinafter, the case where, in a system corresponding to IPv4, mobile node MN (or partner appliance PA) sends information (data, signals) to partner appliance PA (or mobile node MN) not via home agent HA but via foreign agent FA is expressed as xe2x80x9cto send directlyxe2x80x9d or xe2x80x9cdirect sendingxe2x80x9d.
Thus, communication is established between partner appliance PA and mobile node MN. Thereafter, data from mobile node MN to partner appliance PA is sent directly ({circle around (4)}); whereas data from partner appliance PA to mobile node MN is sent via home agent HA and foreign agent FA ({circle around (1)}, {circle around (2)} and ({circle around (3)}).
FIGS. 15 and 16 show conventional procedures for establishing communication between partner appliance PA and mobile node MN in the case of IPv6. In FIGS. 15 and 16, the communication procedures are shown as {circle around (1)}-{circle around (4)}. {circle around (1)}-{circle around (4)} shown in FIG. 15 correspond to {circle around (1)}-{circle around (4)} shown in FIG. 16.
FIG. 16 shows a system to which the Mobile IP corresponding to IPv6 is applied. The configuration of the system in FIG. 16 is identical to that shown in FIG. 14, and therefore, detailed description thereof is not repeated. Referring to FIG. 16, mobile node MN has home address HAD while it is connected via IP sub-network 10 to home agent HA. When the mobile node MN that was connected to home agent HA via IP sub-network 10 moves in a direction indicated by the dashed arrow AR and comes to be connected to a foreign link (not shown), mobile node MN acquires a moved address MAD, i.e., a temporary IP address as a global address, from a server (not shown) on communication network NE, although the way of acquiring the moved address MAD is not limited thereto. Mobile node MN then notifies home agent HA of that moved address MAD as care of address CAAD indicating its current location. Thereafter, the message from partner appliance PA for mobile node MN is sent as follows.
Referring to FIG. 15, partner appliance PA sends xe2x80x9ccall setup requestxe2x80x9d to home agent HA for a message according to Q.931, etc. ({circle around (1)}). Home agent HA receives the call setup request, and sends it to mobile node MN by tunneling ({circle around (2)}). Mobile node MN, in response to receipt of the call setup request, directly sends xe2x80x9ccall acceptedxe2x80x9d, xe2x80x9ccallxe2x80x9d and xe2x80x9cresponsexe2x80x9d to partner appliance PA ({circle around (3)}). Thus, connection between partner appliance PA and mobile node MN is established. Thereafter, data from partner appliance PA is sent to mobile node MN via home agent HA by tunneling ({circle around (1)}, {circle around (2)}); whereas data from mobile node MN is sent directly to partner appliance PA. Here, at an appropriate timing, mobile node MN notifies partner appliance PA of xe2x80x9cbinding updatexe2x80x9d ({circle around (3)}), as will be described later, by sending it directly. Once mobile node MN receives its response (xe2x80x9cbinding acknowledgmentxe2x80x9d) from partner appliance PA ({circle around (4)}), a direct connection between partner appliance PA and mobile node MN is established. Thereafter, like the data from mobile node MN to partner appliance PA, data from partner appliance PA is sent directly to mobile node MN ({circle around (4)}), rather than being sent by tunneling via home agent HA. Hereinafter, the case where, in a system corresponding to IPv6, mobile node MN (or partner appliance PA) sends information (data, signals) to partner appliance PA (or mobile node MN) not via home agent HA or foreign agent FA is expressed as xe2x80x9cto send directlyxe2x80x9d or xe2x80x9cdirect sendingxe2x80x9d.
The expression reading xe2x80x9cto notify of binding updatexe2x80x9d means that, in a mobile communication according to IPv6, mobile node MN notifies partner appliance PA of its moved address MAD at a certain timing after transmission between mobile node MN and partner appliance PA has started via home agent HA.
Another technique regarding the mobile communication is disclosed in Japanese Patent Laying-Open No. 10-51449, wherein communication is established by dynamically altering communication protocol addresses (IP addresses) along with movement of a computer. In this reference, an address management server collectively manages tables for home addresses and moved addresses, and a sending terminal has an address table cache that is cleared according to a lapse of time. On the sending terminal side, when data to be sent is supplied from a corresponding application, a socket hook processing unit snatches away a send-to address added to the relevant sending data, and if the address table cache is cleared, makes an inquiry to the address management server, and, according to the inquired result, converts the send-to address to an appropriate address if necessary. Thus, the application is allowed to communicate without noticing the change of addresses.
According to the technique disclosed in the reference as described above, however, it is necessary to inquire the address management server, separately, so as to find the current address, which increases traffic. Further, in the method for controlling communication between partner appliance PA and mobile node MN under IPv4 as shown in FIGS. 13 and 14, data from partner appliance PA for mobile node MN after its movement is constantly sent by tunneling via home agent HA. Thus, the communication path becomes redundant, causing delay in communication. Accordingly, transmission of application data for images and sounds for which real-time data transmission is required depends on where mobile node MN has moved, thereby causing degradation in quality of the transmission data. In other words, time lag between data sending/receiving by partner appliance PA and mobile node MN becomes considerable, which makes it difficult for the mobile node MN to synchronously reconstruct and process the application data.
Further, with the method for controlling communication between partner appliance PA and mobile node MN under IPv6 as shown in FIGS. 15 and 16, the redundant communication path as described above is prevented by the binding update. However, the timing at which the direct sending between partner appliance PA and mobile node MN becomes available by the binding update is determined by a policy of network designing, regardless of whether the data requires real-time processing or not. Thus, delay inevitably occurs when transmitting data involving images, sounds and the like that requires real-time transmission and real-time processing.
In view of the foregoing, in the communication control method for the Mobile IP under IPv4 or IPv6, improvement is desired in communication control procedures between partner appliance PA and mobile node MN when mobile node MN moves and comes to belong to a network segment that is distant from home agent HA. Specifically, communication control procedures are desired which prevent delay in sending/receiving data of images, sounds and the like (e.g., data being sent via IP telephone or video telephone) that would be easily affected by transmission delay in communication.
An object of the present invention is to provide system and method for mobile communication that avoid transmission delay of data for which real-time transmission is required.
To achieve the object, in the mobile communication system according to an aspect of the preset invention, a communication terminal that communicates with a mobile terminal to send data to the mobile terminal and a prescribed station that relays communication between the mobile terminal and the communication terminal are connected to each other via a communication network. The mobile terminal communicates with the prescribed station, and as it moves, it is switched and assigned with a different address for every visited area, for uniquely identifying the mobile terminal in the relevant area.
In the above-described system, the mobile terminal is provided with a call setup request receiving unit, a determination unit and an address notification unit, which operate while the mobile terminal is moving. The communication terminal is provided with a data sending unit.
When the call setup request receiving unit at the mobile terminal receives call setup request information for requesting setup of a call for data transmission from the communication terminal via the prescribed station, the determination unit determines, based on the call setup request information received, whether or not real-time communication is requested for the data. As a result of the determination, if it is determined that the real-time communication is being requested, an address currently assigned to the mobile terminal is notified by the address notification unit to the communication terminal. Upon receipt of the address notification, the data sending unit of the communication terminal sends the data via an established communication path to the mobile terminal, based on the notified address. This established communication path between the mobile terminal and the communication terminal includes the communication network but does not include the prescribed station.
Accordingly, the data for which real-time transmission is required is transmitted via the communication path including the communication network but excluding the prescribed station, or in other words, via a shortened communication path not relayed by the prescribed station. The notification of the address by the address notification unit to the communication terminal is carried out immediately after the call setup request is made. This prevents transmission delay of data for which real-time transmission is required. Further, establishment of the above-described communication path reduces communication load exerted both on the prescribed station and on the communication network.
In the above-described mobile communication system, the address notification unit has an on-the-move address notification unit. While data is being sent from the data sending unit to the mobile terminal, the on-the-move address notification unit notifies the communication terminal of a new address assigned to the mobile terminal with every further movement of the mobile terminal.
Accordingly, the mobile terminal is constantly assigned with new addresses while moving, so that it becomes possible to transmit data continuously, without disconnecting the call having been setup between the mobile terminal and the communication terminal.
In the above-described data communication system, the communication terminal further includes an address storage unit that stores the address notified by the address notification unit corresponding to the call. Every time the address notification unit notifies of a new address, the address stored in the address storage unit is updated using the notified address.
The address is stored in the address storage unit only temporarily. Therefore, the address storage unit can be configured with an inexpensive and simple storage element, e.g., RAM (random access memory), so that the cost of the communication terminal itself can be reduced.
In the above-described mobile communication system, the communication path is established corresponding to the call for which the call setup request information was received by the call setup request receiving unit. When the call is released, the address corresponding to the call is deleted from the address storage unit.
Accordingly, the address storage unit of the communication terminal needs to store the address only while the call is being maintained. Thus, storage capacitance required therefor is relatively small.
In the above-described mobile communication system, the data sending unit prevents failure in receiving packets (hereinafter, also referred to as xe2x80x9cpacket lossxe2x80x9d) during data transmission that may occur every time an address is notified.
Accordingly, even if an address is notified while the data is being sent, the packet loss during the data transmission is prevented, and thus, communication quality is improved. For prevention of the packet loss, the data sending unit may be configured to suspend data transmission whenever an address is notified, or to re-transmit the data.
In the above-described mobile communication system, the communication network may be the Internet. In this case, the communication between the communication terminal and the mobile terminal is carried out in accordance with the Mobile Internet Protocol. The Mobile Internet Protocol may be the one corresponding to Internet Protocol version 4 or Internet Protocol version 6.
The above-described mobile communication system may be configured as follows. Specifically, a plurality of stations including the prescribed station for relaying communication between the mobile terminal and the communication terminal are connected to one another via a communication network. The mobile terminal communicates with the prescribed station, and as it moves, it is sequentially switched and connected to one or more arbitrary stations except the prescribed station among the plurality of stations. During this time, the mobile terminal is assigned with a different address from each arbitrary station to which the mobile terminal is connected, for uniquely identifying the mobile terminal in the relevant area. When the system is configured as above, the call setup request receiving unit has a request information receiving unit, and the data sending unit has a sending unit.
The request information receiving unit receives the call setup request information from the communication terminal via an arbitrary station connected to the mobile terminal, the prescribed station and the communication network. The sending unit sends data to the mobile terminal, based on the notified address, via a communication path established after the address was notified. The established communication path is configured with the communication network and the arbitrary station, but not including the prescribed station.
Accordingly, data for which real-time transmission is required is transmitted via the communication path including the communication network, the arbitrary station to which the mobile terminal is connected, but not including the prescribed station, or in other words, via a shortened communication path not relayed by the prescribed station. The notification of an address from the address notification unit to a communication terminal is carried out immediately after a call setup request is made. Thus, transmission delay of the data for which real-time transmission is required is avoided, and, by establishing the above-described communication path, communication load exerted on the prescribed station and the communication network can be reduced.
In the above-described mobile communication system, the address notification unit includes an on-the-move address notification unit. While data is being sent to the mobile terminal by the data sending unit, every time the nomadic, mobile terminal comes to be switched and connected to a new arbitrary station, the on-the-move address notification unit notifies the communication terminal of a new address assigned to the mobile terminal by the new arbitrary station.
Thus, even if the mobile terminal moves, current addresses are constantly assigned thereto, and thus, it becomes possible to transmit data without disconnecting the call having been setup between the mobile terminal and the communication terminal.
In the above-described mobile communication system, the communication network may be the Internet, and the communication between the communication terminal and the mobile terminal may be carried out according to the Mobile Internet Protocol corresponding to Internet Protocol version 4.
The mobile communication method according to another aspect of the present invention is applied to a mobile communication system wherein a communication terminal for communicating with a mobile terminal to transmit data thereto is connected via a communication network to a prescribed station for relaying the communication between the mobile terminal and the communication terminal, and wherein the mobile terminal communicates with the prescribed station, and as it moves, every time it moves in a different area, it is switched and assigned with a new address for uniquely identifying the mobile terminal in the relevant area. The mobile terminal includes a call setup request receiving step, a determination step, and an address notification step, which are carried out while it is moving. The communication terminal includes a data sending step.
When call setup request information is received at the call setup request receiving step for requesting setup of a call for data transmission from the communication terminal via the prescribed station to the mobile terminal, the determination step determines, based on the received call setup request information, whether or not real-time communication is being required for the data. As a result of determination, if it is determined that the real-time communication is required, the address notification step notifies the communication terminal of a currently assigned address. The data sending step then sends data to the mobile terminal based on the notified address, via a communication path that is established including the communication network but not including the prescribed station after the address was notified by the address notification step.
Accordingly, the data for which real-time transmission is required is transmitted via the communication path including the communication network but excluding the prescribed station, or in other words, via a shortened communication path not relayed by the prescribed station. Further, the notification of the address to the communication terminal by the address notification step is carried out immediately after a call setup request is made. Thus, delay in transmission of data requiring real-time transmission is avoided. Further, by establishing the above-described communication path, communication load put on the prescribed station and the communication network can be reduced.
The above-described mobile communication method is also applicable to the case where the mobile communication system is configured as follows. Specifically, a plurality of stations including the prescribed station as described above for relaying the communication between the mobile terminal and the communication terminal are connected to each other via a communication network. The mobile terminal communicates with the prescribed station among the plurality of stations, and as it moves, it is sequentially switched and connected to at least one arbitrary station except for the prescribed station among the plurality of stations. Every arbitrary station to which the mobile terminal is connected assigns an address to the mobile terminal for uniquely identifying the mobile terminal in the relevant area. When applied to such a system, the call setup request receiving step of the mobile communication method includes a request information receiving step, and the data sending step includes a sending step. The request information receiving step receives the call setup request information from the communication terminal via the arbitrary station to which the mobile terminal is connected, the prescribed station and the communication network. The sending step sends the data to the mobile terminal based on the notified address, via a communication path. This communication path is established after the notification of the address by the address notification step, including the communication network and the arbitrary station, but excluding the prescribed station.
Thus, the data requiring real-time transmission is transmitted via the communication path including the arbitrary station and the communication network but not including the prescribed station, or in other words, via a shortened communication path not relayed by the prescribed station. Further, the communication path is established immediately after the call setup request is made. Thus, transmission delay of the data requiring real-time transmission is avoided, and, by establishing the above-described communication path, communication load exerted on the prescribed station and the communication network is reduced.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.